1. Field of the Invention
The present invention relates to a method of forming a light emitting device with a direct contact lens structure and, more particularly, to a method of directly depositing a liquid epoxy lens material onto the emitting device. The epoxy will naturally flow to assume a convex shape and completely encapsulate the device and a substantial portion of its associated mounting structure.
2. Description of the Prior Art
Semiconductor light emitting diodes have found ever-increasing use as replacements for filament bulbs in a wide variety of applications. Their small size, low power consumption and long life make them attractive for such uses as indicator lamps in key telephone sets and switchboards. Careful consideration must be given in such uses for distributing the light to produce maximum impact on the viewer. Of the light emitted by a p-n junction, only a small fraction exits through the surface of the diode, due to the "critical angle" of the diode material whereby most of the light becomes reflected and absorbed within the diode material. In this regard, the small size of the diode (approximately 11 mils on each side) is a drawback since light is emitted from too small of an area for good viewing. To overcome this problem, it is necessary to spread the light over a larger area while maintaining a sufficient brightness. This may be accomplished, for example, by placing the LED within a cavity which has formed therein a plurality of spherical lenses as disclosed in U.S. Pat. No. 4,013,915 issued to W. H. Dufft on Mar. 22, 1977. The lens arrangement thus produces an array of discrete images which, when combined, enhance visibility and permit good off-axis viewing. Although this arrangement does indeed improve the attributes of the LED, large scale production of LEDs with the plural spherical structure would be extremely time-consuming and expensive.
An alternative arrangement is disclosed in U.S. Pat. No. 3,805,347 issued to N. E. Collins et al on Apr. 23, 1974. In the Collins et al arrangement, an epoxy material with a convex mensicus surface is placed over the diode element. This epoxy material functions both to increase the critical angle of the diode (and hence the amount of light emitted from the diode) and also to focus this increased amount of light toward the lens, the lens being removed a substantial distance from the surface of the diode. As a variation of this technique, a viscous monomer is placed in the lens cap, prior to the lens cap being fitted onto the diode. When mated, the viscous material will deform by gravity to surround the diode and form a conical light director between the diode and the lens.
Although these and other prior art techniques have been helpful in improving the quality of LEDs, their use in large volume production is limited, since a number of processing steps are required to form this additional material over the diode and to subsequently place the lens cap over the arrangement, where alignment between the lens and the diode is an important consideration. Therefore, a need remains in the prior art for an LED assembly with the required characteristics described above which can be produced in a large-scale manufacture environment.